I figured it out.

I added the Ubisoft Connect installer as a non Steam game, installed it with GE-Proton9-4, and then switched the shortcut to the location of "UbisoftConnect.exe".

Then, in the launch options, I put:

PROTON_BATTLEYE_RUNTIME="$HOME/.steam/steam/steamapps/common/Proton BattlEye Runtime" %command% uplay://launch/15657

And make sure the Proton BattlEye runtime is installed through Steam.

I played multiple full matches in a row like this without any issues.

Edit: Oh I almost forgot, you also need to get a copy of pdh.dll and put it in the game's directory.

Haven't tried yet, but I've seen some people on YT claiming to have done so... If you try it out let me know if you succeed!

I got it to work perfectly from this guide: https://piped.video/watch?v=_PLEm1v9bzw Works really well high fps and all. Something I dont think the guide mentions is updating the battle eye runtime using the one from steam.

I have at least successfully started it and played two matches unranked. I run it through Lutris (Start Ubisoft connect from Lutris) and the start xdefiant through Ubisoft connect.

I followed some Indian guys tutorial on YouTube. It crashed two times and trying to start it a third time, Lutris gave an error sth was missing (don't remember what exactly) and offered to install it. After that it worked but probably more coincidence than knowing what I did. The tutorial added two game execution properties and installed some windows dll through winetricks.

I got it to run for one single match and I haven't had any luck since.

Either the game crashes when loading into a match or I get an anti cheat error.

(Update) I got it to work for one more game by using Winetricks to install pdh.dll but after that game it just started crashing again...

Tried a couple times - installing via lutris, or proton, played with some winetricks etc. Eventually the launcher worked, then more tweaks for the game to load. But then gave up once it crashed to desktop loading the game every time.

Its a shame, reasonably fun game overall.